1. Field of the Invention
The present invention relates to a technique for visualizing patterns and characters on a printing medium.
2. Description of the Related Art
As an anti-counterfeit technique or authenticity determination technique of printed matters, a printing method for generating a printed matter which cannot be visually recognized (or is hard to be visually recognized) under ordinary light but can be easily discriminated using a device such as an infrared camera sensitive to an infrared range under infrared light is available.
As a representative printing method, a method disclosed in Japanese Patent No. 3544536 is known. This method uses the fact that only a black (k) color material of color components of cyan (c), magenta (m), yellow (y), and black (k) used in general print processing has large infrared absorption characteristics. That is, an image is printed on a printing medium using black (k) having large infrared absorption characteristics for a latent image region, and using cyan (c), magenta (m), and yellow (y) having small infrared absorption characteristics for a background region. Then, the output printing medium is irradiated with infrared light, and a latent image is discriminated using an infrared camera.
However, with the above method, since a latent image region is formed using only black (k), it is expressed by only a black-based achromatic color. In order to prevent the latent image region from being visually recognized under ordinary light, a background region also has to be expressed by an achromatic color. Hence, a print image is expressed by only black-based achromatic colors, thus posing a problem. For this reason, a print image, which is formed using a plurality of colors, and has the aforementioned latent image region and background region, cannot be generated.